Hematopoiesis is the process of forming new blood cellular elements in vertebrates. In this regard, thrombopoiesis is a hematopoiesis leading to the formation of thrombocytes, which are also called platelets. The process begins with a multipotent stem cell, a hemocytoblast, which gives rise to a common myeloid progenitor cell. The progenitor cell, in turn gives rise to colony forming unit (particularly, CFU-Me, which is also referred to as CFU-Meg or CFU-Mega) fated to become megakaryocytes. The CFU-Me gives rise to megakaryoblasts. A megakaryoblast is the precursor for a promegakaryocyte. The promegakaryocyte, in turn, is the precursor cell for a megakaryocyte. The megakaryocyte is the cell from where the platelets are produced. Platelets are pinched off from the megakaryocyte as cellular fragments. They then move to the peripheral blood. They are essential in blood clot formation and hemostasis.
In summary, a thrombocytic series is a developmental series of blood cells through thrombopoiesis. The thrombocytic series entails the following: hemocytoblast → megakaryoblast → promegakaryocyte → megakaryocyte (source of platelets).